1. Field of the Invention
The subject invention relates to a fabrication method for solar cell assembly, and particularly to a fabrication method for solar cell assembly by using a thermal injection molding process instead of a lamination process.
2. Description of the Related Art
Solar cells which are mostly made from single crystal silicon or poly-crystal silicon are eco-friendly and economical energy alternative, and have become prevalently used in daily life, and for their better and more efficient use, developing large and thin solar cells is needed. Their fragility and thin proportions make them particularly susceptible to damage from strong impacts. Since solar cell electrodes cannot be exposed to the surroundings for a long time during operation, and the working voltage of each individual solar cell is low. It is necessary to connect a plurality of individual solar cells in series or parallel and encapsulate them into a solar cell assembly which may be used independently as a power unit.
The methods presently employed for fabricating solar cells are quite similar. Connecting sheets composed of conductive materials such as copper are used to connect and solder a plurality of solar cell sheets in a discontinuous series manner to form a row of solar cell sheets. Rows of solar cell sheets are connected in parallel to form several sets of solar cell sheets. The following components are laminated from the bottom to the top: a front substrate, such as glass; an encapsulation material; several sets of solar cell sheets; an encapsulation material and a back substrate, such as composite fluoride plastic film (such as commercial available TPT film). The lamination is put into a vacuum laminator and subjected to a vacuum lamination process. The lower chamber of the laminator is vacuumized and then pressurized and heated to integrate the lamination of glass substrate/encapsulation materials/several sets of solar cell sheets/encapsulation materials/back substrate. After the lamination takes shape, the lamination is taken out from the chamber and equipped with a metal frame. A solar cell assembly is obtained.
Conventional lamination processes integrate laminations by performing heating and pressurization treatments. However, pressurization treatments tend to cause deformation, damage and cracking in solar cell sheets. Moreover, when the environment is heated to a temperature above 120° C. during the lamination process, ethylene-vinyl acetate encapsulation materials may be softened, giving rise to the overlapping of parallel-aligned sets of solar cell sheets and diminished efficiency of the solar cell assembly. Further, the toughened transparent glass substrate, which is commonly used in a solar cell assembly, often has a thickness over 3.2 mm and poor surface smoothness after a toughening process. When a solar cell assembly is fabricated by a lamination process with two such toughened glass substrates, the solar cell sheets of a thickness of only 180 to 200 μm tend to break due to the weight and poor surface smoothness of the glass substrates. Therefore, the conventional lamination process is not suitable for encapsulating a solar cell assembly with a transparent glass back substrate and particularly unsuitable for encapsulating large solar cells. Besides, lamination of encapsulation materials is mostly carried out manually. Due to the inaccuracy resulting from manual operation, bubbles tend to be observed in the encapsulation materials and thus render the product uniformity of solar cell assemblies rather poor and the quality of solar cell assemblies unstable. Further, such manual operation also creates problems such as material waste and environmental pollution, and suffers inherently limited productivity.
The subject invention is provided to meet the increasing need for large solar cells, which refer to those having an area greater than 1 square meter, and to address the aforementioned problems. The inventors of the subject application discovered that fabricating solar cell assemblies with a thermal injection molding process instead of the conventional lamination process and using specific equipment and encapsulation materials may avoid the inaccuracies resulting from manual operation, drastically boost the productivity of the process and efficiently reduce the cracking defects in solar cell sheets. The lifetime of a solar cell assembly is also prolonged. The fabrication method of the subject invention is suitable for large and thin solar cells.